Methods of making metal cones for cathode ray tubes



UBES

July 3, 1956 I A. BAUER METHODS OF MAKING METAL CONES FOR CATHODE RAY T 2 Sheets-Sheet 1 Filed Feb. 24, 1951 INVENTOR Andrew Bauer BY 1% M TTORNEY A. BAUER METHODS OF MAKING METAL CONES FOR CATHODE RAY TUBES Filed Feb. 24, 1951 2 Sheets-Sheet 2 AIId I G $53591 METHGDS OF MAKING METAL CONES FOR CATHUDE RAY TUBES Andrew Bauer, (Jamden, N. J., assignor to Radio Cor poration of America, a corporation of Delaware Application February 24, 1951, Serial No. 212,628

4 Claims. (Cl. 29-535) This invention relates to improvements in methods of making cathode ray tubes having composite glass and metal envelopes. More particularly itrelates to improvements in methods of making metal shells for the bulb portions of such tubes.

Recently, as for example, in the invention described in copending application of R. D. Faulkner, Serial No. 120,400, filed on October 8, 1949, now U. S. Patent 2,692,963, issued July 6, 1954 and assigned to the assignee hereof, certain advances have been made in the cathode ray tube art resulting in the successful commercial production of such tubes with composite metal and glass envelopes. The bulb portion of any of the presently available composite types usually comprises two parts: a round metal cone, i. e. one which has circular transverse cross-sections, and a circular glass face-plate sealed into a rim or lip at the large end of the cone.

These prior art composite structures involve a number of disadvantages. A principal disadvantage is that cabinet space is wasted. This results from the inherent inefiiciency of using a round cone and a circular face-plate where the electron beam is to scan through a rectangular solid angle and to trace a rectangular raster. This waste of space becomes progressively more serious as screen sizes increase. It makes cabinets needlessly expensive and complicates theirdesign. Another disadvantage is that round tubes are difficult to mount.

Therefore, it is desirable to provide rectangular types of metal; cones and to make with them cathode ray tube envelopes with rectangular bulbs and face-plates.

Accordingly, it is an object of the invention to provide such cones and methods for making them.

It is a further object of the invention to provide methods for making such cones which afford economical use of the expensive special alloys required to obtain satisfactory glass-to-metal seals in the finished tube.

And it is a further object of this invention to provide methods for making such cones with a minimum of costly manufacturing processes.

In general, these and other objects are attained by using in combination two metal-working operations of different kinds: (1) spinning the central portion of a sheet metal blank over the outside of a hard-surface form shaped as a conical frustum; and (2) forcing the partially formed blank by an outwardly acting means to assume the internal shape of a rectangular female die. In spinning the center portion of a flat metal blank sufficient pressure should be used to reduce it in thickness while imparting to it the shape of the frustum. .ln this step the peripheral portion of the blankmay be left undisturbed extending in its original full thickness from the spun portion like the brim of a hat. The outwardly acting means may be hydrostatic pressure or a male punch having the conjugate shape of the die. This combination of steps results in eflicient use of material since the spinning step thins out a portion of the blank which eventually'forms the part of the cone, its mantle, where the least strength stem" is needed, While the other step forms the other portion into the rim, the sealing flange and a peripheral portion the spinning step whereby it is possible to accomplish the rest in a single operation, such as in one deep draw. The present invention minimizes: the loss of metal as scrap; the required number of machine and machining operations and of annealing steps; and the amount of shrinkit simplifies a later-required step of settling phosphor material on the inside surface of the face-plate.

in the drawing:

Figure 1 is a front view into a rectangular metal cone or shell, embodying the present invention, as seen through the face-plate sealing flange;

Figure 2 is an exterior top or bottom view of a cathode ray tube, partially cut away, which comprises a cone or shell as shown in Figure l with a face-plate sealed into the rectangular flange on the front thereof and a neck fused onto a round flange at its back;

Figure 3 is an exterior side view of the tube shown in Figure l; v

- Figure 4 shows a developed flat metal blank of an approximately oblately circular or generally oval shape which is preferred in making a cone as in Figures 1 and 2 in accordance with the present invention for reducing to a minimum the amount of trimming of excess material from the front edge of the sealing flange which will be necessary after the second metal-Working operation has been completed; and

Figures 5 and 6 show apparatus suitable for re-forining a partly spun blank into'a rectangular cone or shell.

The frusto-pyramidal shell 10 shown in Figures 1, 2, and 3 comprises a principal portion herein designated as the mantle 11, and two other portions between which the mantle extends, namely a small round sealing flange 12, at the back of the shell, to which a neck 13 may be fused, and a large rectangular flange 14, at its front, into which the face-plate 15 may be sealed to form an envelope for a cathode ray tube. In Figures 2 and 3 there is shown a point P which represents the center of deflection of the electron beam Within the sealed tube envelope.

Unlike a round cone, the frusto-pyramidal shell lid of electron beam deflection required to scan a rectan ular ing in some areas, resulting in splits or cracks, and/or excessive gathering (of the incompressible material) in others, resulting in folds and pleats. However, ac cording to -"the present invention, this "can be accomplished provided the included angle of the frusto-conical portion of the blank (16, Figs. Sand 6) which is produced by the spinning operation is appropriately smaller than the largest included angle of the rectangular shell and larger than its smallest included angle, e. g. if it is 60 for the cone shown in Figures 1-3. If this is so, then in the reforming operation the slack developed by pushing together opposite points on the round opening of the conical blank to form the top and bottom of the rectangular opening of the frusto-pyramidal shell can be taken up by the pulling apart the sides of the rectangular opening of the frusto-pyramidal shell.

At the present state of the art certain chromium bearing alloys are the preferred materials for kinescope cones, even though they are more difiicult to work and more expensive than other materialssuch as cold rolled steel. One reason for which they are preferred is that their expansion-contraction characteristics are appropriately related to those of suitable types of glass for generating certain useful compressive forces, therein, during the manufacturing process, and for not generating certain harmful tensile forces. For example, useful compressive forces are produced in the face-plate by shrinkage of the sealing flange around it after sealing-in. This causes the face-plate to bulge outward improving its ability to oppose the inwardly acting force of atmospheric pressure which becomes effective upon evacuation. Another reason is that the chromium in these alloys produces an oxide film on the sealing flanges when they are heated for sealing-in, and, due to the solubility of chromium oxide in molten glass, a good glass-to-metal seal is formed. However, chromium not only is an expensive ingredient in these alloys but also makes them more difiicult and expensive to roll into sheet material and to work into finished articles. As a result the metal shell is usually the principal item in the over-all cost of glass-and-metal picture tubes, particularly those having large screens since their cones may easily weigh 12 to pounds. Obviously, therefore, in these tubes it is very important to avoid using more metal material than is really necessary. The problem was met for the manufacture of round cones first by the use of high pressure spinning, such as that described in U. S. Reissue 19,790, and then by the invention set forth in the abovementioned copending application. As' is well known the effect of high pressure spinning over a round conical mandrel is to thin out the material, by an amount which is a function of the sine of the included angle, thereby effectively causing a given weight of material to extend over a larger portion of the area of the cone than if it were fabricated in some other way such as by drawing. In general, the blank material must be thick enough so that the face-plate sealing flange as formed without thinning will be strong enough. Because of this, and since the amount of thinning obtainable in the mantle is limited, many cones, even though they were spun under high pressure have had thicker side walls than necessary and therefore havebeen somewhat wasteful of material. However, further economy was made possible, as taught in the above-mentioned copending application, Serial No. 120,400, by an improved structural design which permits fabrication of the cone from a thinner blank than formerly. In a cone of this design the walls of the mantle as formed of the thinner blank and as further thinned by spinning are no longer too heavy and yet the sealing flange is sufficiently strong because it is reinforced byan adjacent portion of the mantle which is' spun-at a sufiiciently reduced pressure to be approximately as thick as the flange.v

According to the present invention it is possible to make a frusto-pyramidal shell so as tages both of sine law spinning-and of the feature set forth in the abovementioned eopending application.

Part of the apparatus requiredt'o practice. the presentlydisclosed method of making frusto-pyramidal shellsis adequately shown in the patent and the patent applica tion referred to above. It comprises a rotatable form shaped as'a conical frustum of hard-surfaced material, onto the small: end of a flat blank may be :attaehed. and keyed so as to be; rotated therewitmand oner to attain the advanmaximum heights, widths,

or more rollers for progressively urging successive portions of the blank under very great pressure against the outside surface of the frustum starting near its small end and progressively advancing down the side thereof toward its base to force material ahead of it and to spin it into the shape of the conical frustum form. According to the present invention such apparatus is not utilized for processing as much of the flat blank as in forming a round metal cone. Instead only a center portion of the blank is spun to form thereof a hollow conical frustum (16, Figs. 5 and 6) of a depth which is smaller than, and preferably bears a predetermined relationship, to the desired depth for the finished rectangular shell. Among different specific shells this relationship will vary as a function of differences in a number of their parameters such as the aspect ratios of their face-plates, their respective included angles, their etc. However, for a frustopyramidal shell proportioned as in Figures 1-3 the preferred ratio of the depth of the spun frustum 16 to that of the complete cone, 10, is of the order of 7 to 8%.

Apparatus for the spinning operation of the present invention is not shown herein since a number of suitable kinds are already known. However, two kinds of apparatus for performing the other operation are shown in Figures 5 and 6 respectively. The manner in which they are used is explained below.

The approximately oblately circular or generally oval blank 17 is cut from sheet metal stock so that the grain thereof, as represented by an arrow in Figure 4, extends in the direction of its minor axis. This is done because the second metal working operation can be accomplished with more uniform results and less shrinkage losses if the partially formed blank 20 is so oriented with respect to the female die that a line corresponding to the original grain of the stock extends crosswise to the large open end of the die rather than lengthwise thereto. A round hole 18 is provided at the center of blank 10, i. e. at the intersection of its major and minor axes. This hole is'intended to fit snugly over a short cylindrical arbor which protrudes from the small end from the hard surfaced frustum used in the spinning operation and which, as shown in the above-mentioned copending application, may be threaded to provide a means for clamping the blank onto the frustum. Two other holes, 19, are provided for engaging off-center pins which may also protru e from the small end of the frustum, which serve for keying the blank thereto so that they will rotate together. An indicator means, such as a small hole 22, or a row thereof, may be provided to indicate the direction of the grain. Since the blank is very nearly round, i. e. although generally oval the ends thereof are semicircles, this will be helpful for an operator and will tend to shorten the time he will require to properly orient a partially formed blank 20 in the stamping mill. In the stamping mill represented in Fig. 5, a female die 21 is mounted on the bottom, free end of an hydraulicly actuated. piston 24 with its hollow interior directed downward. A male punch 25 is rigidly supported on a base 26 so that it points upward with its axis coinciding with that of the piston 24.

Before reforming the blank 20 on the stamping mill, it preferable to anneal it and to provide it with a surface lubricant or drawing compound. Satisfactory annealing of a partially formed blank of A inch stock has been accomplished in 6 minutes at 1650 degrees Fahrenheit. This sufficiently eliminates a tempering effect which is incurred in the spinning operation. Water soluble soap types of lubricant are quite suitable and have the advantage that they are readily. removable from the finished product by washing it in water.

After the partially-formed blank 20 has been annealed and dipped in lubricant it is placed on the punch 25 as shown in Fig. 5 and then the female die is brought down upon it with a suflicient pressure to reform it in a single draw.

It has been found that a 560 ton impact or mechanical type of stamping mill is adequate for reforming a partially-formed blank 20, which has a maximum Wall thickness of .1 inch at the flange and consists of 17 per cent chromium bearing iron aHoy, into a rectangular cone whose sealing flange has a 17 inch diagonal. However, if an hydraulic stamping mill is used, it should be heavier. Moreover, whatever the type of mill, faster and more satisfactory results will be obtained if its capacity substantially succeeds the permissible minimum. If desired the male punch 25 may include as a protrusion from the center of its top surface, a short cylindrical cutter 27 which in cooperation with a sharp-edged cylindrical socket 28 correspondingly located in the female die may serve for piercing the neck opening 23. This opening, which corresponds to the area enclosed in a dotted circle in Fig. 4, is about /2 inches in diameter in the 17 inch diagonal cone mentioned above. However, the preferable way of practicing the present invention is to pierce the center hole in a separate operation following the reforming one. The reason for this is that if the piercing of this hole is accomplished as part of the reforming operation in mass production, a certain inefliciency will result from the necessity of periodically taking these important machine tools out of operation in order to resharpen the cutter 27 and the socket 28. Moreover, the partially-formed blank will be somewhat less free to shift about so as to accommodate itself to the progressively lessening space between the punch and die during reforming if any part thereof becomes captive too early in the operation as may be the case where the piercing operation is combined with reforming.

In order most successfully to form a rectangular cone without cracks and/or pleats and with smooth contours as shown in Figures l3, the following are some of the precautions which should be taken: the included angle of the spun frustum 16 should bear the proper relationship to certain reference included-angles for the desired rectangular cone; the depth of the frustum 16 should bear the appropriate ratio to the depth of the desired finished cone; and the die and punch should be shaped to impart to the top, bottom, and side panels of the rectangular cone a degree of convexity whereby they will constitute out wardly curved panels.

The last of these precautions offers several advantages: it helps to take up slack, gathering, which tends to develop in the reforming operation; it results in a geometrical shape which affords great side wall strength to withstand atmospheric pressure and to minimize flange distortions and seal ruptures as a result thereof; and it provides a bulb shape, for the finished envelope, which does not complicate the operation of applying a fluorescent screen to the face plate by a corner-settling problem.

If these precautions are taken a smooth mantle will result. However, it is diflicult to produce the rather complex configuration of the face-plate sealing flange in a single forming operation without incurring the formation of small irregularities on its inside sealing surface, i. e., such as small wrinkles and folds. For this reason it is advantageous to perform a coining operation for reforming the large sealing flange. The punch and die employed for coining may be very much like those shown in Figure 5 with appropriate portions of their surfaces cut back to clear the cone in the region of its mantel and small sealing flange. As a result the full pressure of the stamping mill will be brought to bear on the large sealing flange to provide the very high pressure per unit area needed for coining. After coining the drawing compound may be washed ofl with water.

While it may seem desirable to anneal the cone after the reforming operation in order to relax strains built up in that operation, this has the disadvantage that it may However, where such a if it is followed by the coining be at least partly restored to finish-grinding. However, it has been found to be prefervable to saw it from the lip on a high speed metal band saw such as a Duall. In doing this, it is advantageous to mount the rectangular cone in a fixture permitting the entire cone to be rotated about an axis corresponding to that of the neck 13 whereby to progressively feed the lip into the saw blade at the point where it passes thru the band-saw table. This axis of the fixture should be angularly movable in a vertical plane about a pivot which is spaced back from the intersection of the saw blade and the table by a distance substantially equal to the radius of curvature of the face-plate 15, i. e., 30 inches for a 17 inch diagonal tube, to permit the rim to rest on the table for all rotational positions of the cone. The result of trimming with such a fixture will be that the lip 29 will have the smoothly undulant edge shown in Figs. 2 and 3. This operation should be followed by a step for removing the burr left by the bandsaw, a suitable cutting means for doing this being a conventional canvas hard wheel charged with abrasive.

Fig. 6 shows an alternative apparatus for the operation of reforming the partiallyformed blank 20. It comprises a die 30 which has the same interior configuration as the die 21 but which, as shown, is employed with its large opening facing upward. A plug 31 is used for closing the holes 18, 19, and 22. The plug comprises a somewhat mushroom-shaped bolt 32, a rubber gasket 33, a heavy washer 34, and a nut 35. The head of the bolt 32 maybe shaped as shown to guide the direction of expansion of frustum 16 into the die. The apparatus of Fig. 6 also comprises a heavy cover 36 carrying a rubber sealing ring 37 fitted into an ovately circular groove 38 in its lower surface. To reform the blank 20 the plug 31 is attached to it; it is placed in the die 30 as shown; and the cover 36 is forced heavily down against it whereby the space inside of the frustum 16 is entirely sealed. Then liquid, such as thick oil, is forced under extremely high pressure from a pump 39, thru a passageway 40, and into the frustum 16 to force it to expand outwardly until it fills the die 30.

As is most clearly shown in Figs. 2 and 3 one result of producing a rectangular cone according to the present invention is that a portion 41, of the mantel 11 adjacent the face-plate sealing flange 14 is formed without thinning, i. e., it is as thick as the original fiat blank 1']. According to the teachings of the above-mentioned copending application this structural feature lends such support to the sealing flange that in making the cone it is possible to start. out with thinner material than would otherwise be possible and therefore wastage of metal in the mantel can be avoided.

Since the sealing surface of the flange 14 intercepts a spherical surface having the center of curvature of the face plate 15, this plate may be preformed with the configuration of a true spherical section. If this is done, its shape will be only slightly atfected when it settles down into the flange 14 during sealing-in and the resulting glassand-metal structure will have great strength to withstand external air pressure.

The spinning step of the method set forth above may be modified by employing a mandrel, the hardened working surface of which has approximately, rather than exactly, the shape of a frustum. That is to say, while the working surface must be a figure of revolution, the slope of the sides does not have to be along a straight line but instead may be along. a line which curves either inward or outward with respect to the axis ofrotation. Moreover, the slope of the sides may be straight for part of the way and then curved. For example, the sides may slope downward along. a straight line in the fashion of a true frustum and then curve outward so that it merges gradually into a fiat or more obtuse frusturn shaped rim portion of the hat-like partially formed blank.

While the face-plate sealing flange presents an undulant profile as the cone is viewed laterally, it is within the scope of the present invention to form the flange with a flat edge. A cone with such a flange if laid on a flat surface with its large opening: facing downward would rest uniformly onthe surface all the way around the flange. Obviously, if the cone is to be made this way, the die used for reformingv apartially formed blank would have to be modified accordingly and this would also be true for a die and punch used for coining. While a fiat faceplate can be used with such a cone if it is made thick enough to have the requisite strength, it is preferable to provide the needed strength by forming the plate to be outwardly curved. Such a plate can be made by supporting a flat glass blank on a flat rectangular frame by its edgesv only and heating it until the center of the blank sags down within the frame. Of course, such a plate is turned over before it is placed in the cone sealing flange preparatory to sealing in. 9

Another possibility is to form the cone with outwardly undulant profiles for the two short sides of its face-plate sealing-flange and straight profiles for the two long sides thereof. In this case the face-plate has the shape of a rectangular section cut out of a cylinder of glass rather than out of a sphere. This form has the advantage that almost all of any ambient room light which may fall on the outside surface of the television picture tube face-plate will be reflected either upward or downward and hence out of the field of vision.

What is claimed is:

l. The method of fabricating a hollow frusto-pyramidal metal shell comprising the steps of: spinning the central portion of a sheet metal blank over the outside of a hard surfaced conical frustum form with sufficient pressure to reduce the metal blank in thickness while imparting to the metal blank a hollow conical frustum portion, in a single operation forming the hollow conical blank portion with successively larger sections progressively more and more oblately-circul'ar and the part corresponding to the peripheral portion of the original blank, without reducingv it in thickness, into a substantially rectangular opening which is an extension of the outwardly extending walls of the frustuni which extension comprises a face-plate sealing-flange; and coin-stamping said sealing flange under much higher pressure per unit area than. that employed in the deep drawing step to more exactly attain for said flange a surface intercepting a spherical surface.

2. The method of forming a hollow frusto-pyramidal shell, said method comprising the steps of, forming a flat oblately circularblankof sheet metal, spinning the central portion of said blank over the outside of a hard frustoconical body to form a frusto-conical portion having an included angle between the smallest and largest included angles of the finished frusto-pyramidal shell, forming the peripheral portion of said blank into a rectangular opening having a flange extending substantially radially from the axis of said opening, coin stamping said flange to more exactly form the flange with a surface intercepting a spherical surface.-

3. The method of working sheet metal of a refractory iron alloy toform a hollow rectangular truncated metal shell, said method: comprising. the steps of, forming a substantially oblately circular blank from a rolled metal sheet with the direction of the short axis of said blank corresponding to the grain imparted to the metal in rolling it, forming an indicator on said blank oriented with said grain direction, spinningv the central portion of said blank over the outside of a hard surfaced conicai frustum with sufficient pressure to reduce it in thickness thereby forming. a hollow conical frust'uni of said central portion with an unthinned peripheral'portion of the blank extending therefrom, orienting said hollow conical frustum with respect to a female die having a large rectarigularly shaped opening with said indicator so that said grain of the metal of said hollow frustu'm' is crosswise to the rectangular opening of said die, reforming the central portion of said hollow frustum in a single draw to conform with the inside surface of said die and simultaneously reforming the peripheral unthinned portion of said blank to conform with the rectangular opening of said die.

4. The method set' forth in claim 3 in which the process of spinning said blank includes forming said hollow conical frusturn with an included angle having a value between the smallest and largest included angles of the desired rectangular truncated shell.

References Cited in the file of this patent UNITED STATEs PATENTS 

1. THE METHOD OF FABRICATING A HOLLOW FRUSTO-PYRAMIDAL METAL SHELL COMPRISING THE STEP OF: SPINNING THE CENTRAL PORTION OF A SHEET METAL BLANK OVER THE OUTSIDE OF A HARD SURFACED CONICAL FRUSTUM FORM WITH SUFFICIENT PRESSURE TO REDUCE THE METAL BLANK IN THICKNESS WHILE IMPARTING TO THE METAL A HOLLOW CONICAL FRUSTUM PORTION; IN A SINGLE OPERATION FORMING THE HOLLOW CONICAL BLANK PORTION WITH SUCCESSIVELY LARGER SECTIONS PROGRESSIVELY MORE AND MORE OBLATELY-CIRCULAR AND THE PART CORRESPONDING TO THE PERIPHERAL PORTION OF THE ORIGINAL BLANK, WITHOUT REDUCING IT IN THICKNESS, INTO A SUBSTANTIALLY RETANGULAR OPENING WHICH IS AN EXTENSION OF THE OUTWARDLY EXTENDING WALLS OF THE FRUSTUM WHICH EXTENSION COMPRISES A FACE-PLATE SEALING-FLANGE; AND COIN-STAMPING AND SEALING FLANGE UNDER MUCH HIGHER PRESSURE PER UNIT AREA THAN THAT EMPLOYED IN THE DEEP DRAWING STEP TO MORE EXACTLY ATTAIN FOR SAID FLANGE A SURFACE INTERCEPTING A SPHERICAL SURFACE. 